Utilizing activated biochar for contaminant removal in dairy processing plant wastewater

Introduction

The dairy industry in India is the largest globally, accounting for 23% of global milk production. The industry contributes 5% to the national economy and directly supports more than 8 crore farmers. Total Milk production in the country is estimated as 230.58 million tonnes during 2022-23 registered a growth of 22.81% over the past 5 years which was 187.75 million tonnes in 2018-19 (Anon., 2023) [2] . Dairy processing plants can be characterized by intensive water consumption and high pollution potential (Duarte et al., 2016). In general, wastes from the dairy processing industry contain high concentration of organic material as biological oxygen demand (BOD) and chemical oxygen demand (COD), suspended solids (SS), nutrients, suspended oil and/or grease, and large variations in pH (Demirel et al., 2005; Luo et al., 2011) [6,14] . So, treatment of dairy processing wastewater is important to prevent and minimize its effects on the environment. Biochar's application in wastewater treatment is broadly categorized into organic and inorganic remediation. Biochar, derived from carbon-rich biomass through pyrogenic black carbon, is gaining attention for its multifunctionality, including carbon sequestration, soil fertility enhancement, bio-energy production, and environmental remediation (Mohan et al., 2014) [17] . Biochar's porosity and functional groups are crucial for diverse applications, but unmodified biochar faces limitations with its small surface area and poor pore properties (Tan et al., 2016) [21] . Raw biochar exhibits limited adsorption capacity for contaminants in concentrated wastewater (Nair and Vinu, 2016; Yao et al., 2013) [18,23] . Activating biochar has garnered scientific attention for better environmental applications, particularly through physical and chemical activation techniques (Lee et al., 2018). Activated biochar finds applications in soil remediation, particularly for removing organic pollutants and heavy metals through absorption (Ahmad et al., 2014) [1] . Activated biochar is highly effective for dairy plant wastewater treatment due to its high surface area and adsorption capabilities, removing contaminants like organic compounds, heavy metals, phosphorus, and nitrogen. It stabilizes pH, mitigates odors, and requires minimal energy, repurposing agricultural waste for sustainable, cost-effective treatment. Its longlasting performance and ability to target specific contaminants make it a valuable addition to wastewater treatment systems. (Logan et al., 2022) [12] .

Materials and Methods

Water sample collection

The effluent was collected in plastic cans from the Dairy processing plant near Junagadh city, Junagadh, Gujarat. The samples were preserved below 4ºC temperature. The samples were brought to the Food testing laboratory-JAU, and the physio-chemical analyses was conducted as per standard prescribed methods.

Physio-Chemical Analysis of Wastewater pH

Glass electrode digital pH meter was used to measure the pH of the wastewater sample before which it was calibrated using the electrometric method.

Electrical Conductivity (EC)

Digital Electrical conductivity meter was used to measure the EC of the wastewater before which it was calibrated with different standards (Richard, 1954) [20] .

Total Dissolved Solids

Digital TDS meter was used to measure the TDS of the wastewater before which it was calibrated with different standards (Howard, 1933) [10] Gravimetric method.

Turbidity (NTU)

It is a measure of cloudiness of water. Turbidity meter is an instrument for measuring and comparing the turbidity of liquids by passing light through them and determine how much light is reflected by the particles in the liquid. The normal measuring range is 0 to 100 is expressed as Nephelometric Turbidity Units (Mhaske et al., 2014) [15] .

Total Suspended Solids (TSS)

The total suspended solids were measured using the Gravimetric method. The principle involved is evaporation of the liquid at 103-105 ℃ (APHA, 1998) [4] . TSS mg/l = (A-B) * 1000/ Sample volume (ml)

Chemical Oxygen Demand (COD)

Indian Standard methods of sampling and test (physical and chemical) for water (APHA, 2005) [5] method was used to analyze the COD in the samples.

Calculation,

Where, A = ml of titrant required for titration against blank, in ml B = ml of titrant required for titration of sample, in ml Biochemical Oxygen Demand (BOD) Azide Modification of Iodometric method as explained in APHA (2000) was used to measure BOD content present in the samples.

Calculation, BOD (mg/L) = 𝐷𝐷 1 -𝐷𝐷 2 ×𝐷𝐷 𝑓𝑓 Where, 𝐷𝐷 1 = DO of diluted sample immediately after preparation (mg/l).

𝐷𝐷 2 = DO of diluted sample after 5 days' incubation at 20 ℃ (mg/l).

𝐷𝐷 𝑓𝑓 = Dilution factor

Total Kjeldahl Nitrogen Total nitrogen was estimated by Kjeldahl method as explained in Physio-Chemical Examination of Water Sewage and Industrial Effluents. However, Salicylic acid thiosulphate modification of Kjeldahl method was used to convert all forms of nitrogen to ammonia. Procedure Digestion: 25.0 ml of the sample was taken in Kjeldahl flask and 25.0 ml of Conc. Salicylic-𝐻𝐻 2 𝑆𝑆𝑆𝑆 4 acid, 1.0 ml copper sulphate solution, 5.0 g potassium sulphate and 5.0 g sodium thiosulphate were added into it. The sample was then digested for 3-4 hours until the solution became clear.

Distillation:

The contents of the flask were transferred into a distillation flask. The solution in the flask was made alkaline with sodium hydroxide and 2-3 drops of phenolphthalein indicator was added to it. The distillation was started after immersing the tip of the condenser in 50.0 ml of boric acid solution in a conical flask. Finally, the distillate was collected in the conical flask. Titration: 0.5 ml of methyl red indicator solution was added to the distillate. It was then titrated against 0.02 N 𝐻𝐻 2 𝑆𝑆𝑆𝑆 4 .Titration was continued until the red color of the solution appeared. A blank sample was also taken and all steps from the digestion step to the final titration was followed.

Total Phosphorus

For phosphates estimation, reagent "A" (added 1 g of ammonium molybdate, 0.02 g of potassium antimony tartrate in 1000.0 ml measuring flask. Then 16 ml of concentrated sulphuric acid will be added to the contents and then distilled water will be added slowly. Finally, the contents will be allowed to dissolve by shaking) and reagent "B" (dissolved 0.88 g of ascorbic acid in 1000.0 ml of reagent "A") will be prepared. Reagent "B" will be prepared freshly (should be prepared freshly) and 4 ml of this reagent "B" will be added to water sample. Made up the volume up to 25 ml with distilled water and absorbance of the color will be measured at 630 nm wavelength in spectrophotometer.

Heavy metals

Nitric acid-hydrochloric acid method was used for digestion of water sample for heavy metal analysis as suggested by APHA (2000). 50.0 ml of acid preserved sample was mixed with 3.0 ml conc. H𝑁𝑁𝑆𝑆 3 . The beaker was placed on a hot plate and heated till volume was reduced to 50%. After cooling, 5.0 ml of conc. H𝑁𝑁𝑆𝑆 3 was added to the digested water sample and again heated till the content of the beaker was reduced to 5.0 ml. Followed by addition of 10.0 ml of HCl and 15.0 ml of water to it and allowed to heat for another 15 minutes. The contents were filtered and centrifuged. The filtered solution was directly aspirated and concentration of the trace metals was analysed through Atomic Absorption Spectrophotometer (AAS). Specific hollow cathode lamps were used for analysis of different metals. The elements chosen for analysis was zinc (Zn), cadmium (Cd), iron, copper, nickel and lead (Pb) because these are ubiquitous pollutants present in the wastewater.

Activated Biochar Collection

After Measurement of Dairy processing plant wastewater Physio-chemical characteristics, for waste remove experiment Process pyrolysis Activated Biochar of raw material cotton stalk collect from REE Department, CAET, JAU.

Process modification at various adsorbent dose and residence time

In this wastewater treatment experiment, a known quantity of prepared biochar (2gm, 6gm and 10gm) was introduced into the wastewater samples (1000 ml) with the aim of mitigating contaminants. Thorough mixing, facilitated by a digital shaker, ensures optimal contact between the biochar and contaminants. The mixture was allowed to interact for a specified contact time (1hour, 2hours and 3hours), during which gentle agitation may be employed to enhance the biochar's adsorption capabilities. Subsequently, the treated water was separated from the biochar using Whatman No. 4 filter paper, and the collected water was subjected to physiochemical analysis. The concentrations of contaminants in the treated water were measured and compared with initial concentrations to gauge the extent of contaminant removal.

Removal Efficiency

Statistical Analysis

Statistical analysis was carried out by the Factorial Complete Randomized Design (FCRD) method in which the effect of various treatments on various parameters was analyzed (Panse and Sukhatme, 1967) [19] .

Results and Discussion

The results of the experiments conducted on "Application of Activated Biochar as an Absorber for Removing Contaminants of Dairy Processing Plant Wastewater" have been described. The observations recorded for water quality parameters and the biochar used were analysed statistically and are presented with the help of tables and figures. The discussions have been made with the significant experiment results obtained during the course of investigation are mentioned in this chapter.

Initial Physio-chemical characteristics of Dairy Processing Plant wastewater

The Wastewater sample was collected from Dairy Processing Plant near to Junagadh city and the initial characterization of the effluent was done. The initial concentrations of various parameters of the effluent were found to be present above the permissible limits. The analysed results are shown in the [6,14] .

Effect of various treatments on TDS concentration

The initial concentration of TDS in the wastewater sample was found to be about 1060.75 mg/l. The experimental results are shown in the Table 3.5 and comparative graph of removal efficiencies of Chemically and Physically activated biochar are shown in the Figure 3.3. For 2g, 6g and 10g of Physically activated and Chemically activated biochar in higher retention time of 3 hours, the removal efficiencies were found to be 14.80%, 22.03%, 26.74% and 8.38%, 17.91%, 24.57% respectively.

Effect of various treatments on TSS concentration

The initial concentration of TSS in the wastewater sample was found to be about 473.665 mg/l. the highest TSS removal efficiency of about 67.86% and similarly, Chemically activated biochar had the TSS removal efficiency of about 65.38%.

Effect of various treatments on Turbidity concentration

The initial concentration of Turbidity in the wastewater sample was found to be about 133. Among the various treatments carried out, it was concluded that Physically activated biochar with 10g/l of the wastewater used in the retention time of 3 hours had the highest turbidity removal efficiency of about 75.99% and similarly, Chemically activated biochar had the turbidity removal efficiency of about 75.66%. The experimental results are shown in the Table 3.7 and comparative graph of removal efficiencies of Chemically and Physically activated biochar are shown in the Figure 3.5. For 2g, 6g and 10g of Physically activated and Chemically activated biochar in higher retention time of 3 hours, the removal efficiencies were found to be 47.76%, 60.09%, 75.99% and 43.22%, 56.39%, 75.66% respectively.

Effect of various treatments on COD concentration

The initial concentration of COD in the wastewater sample was found to be about 1110.5 mg/l. Among the various treatments carried out, it was concluded that Physically activated biochar with 10g/l of the wastewater used in the retention time of 3 hours had the highest COD removal efficiency of about 71.81% and similarly, Chemically activated biochar had the COD removal efficiency of about 67.91%. The experimental results are shown in the Table 3.8 and comparative graph of removal efficiencies of Chemically and Physically activated biochar are shown in the Figure 3.6. For 2g, 6g and 10g of Physically activated and Chemically activated biochar in higher retention time of 3 hours, the removal efficiencies were found to be 51.64%, 61.90%, 71.81% and 50.01%, 58.23%, 67.91% respectively.

Effect of various treatments on BOD concentration

The initial concentration of BOD in the wastewater sample was found to be about 406.5 mg/l. Among the various treatments carried out, the highest BOD removal efficiency of about 73.43% and similarly, Chemically activated biochar had the BOD removal efficiency of about 72.82%. The experimental results are shown in the Table 3.

Effect on Phosphorus

The initial concentration of Phosphorus in the wastewater sample was found to be about 54.985 mg/l. Among the various treatments carried out, it was concluded that Physically activated biochar with 10g/l of the wastewater used in the retention time of 3 hours had the highest phosphorus removal efficiency of about 70.45% and similarly, Chemically activated biochar had the phosphorus removal efficiency of about 65.45%.

Effect on Lead

The initial concentration of Lead in the wastewater sample was found to be about 2.04 mg/l. Among the various treatments carried out, it was concluded that Physically activated biochar with 10g/l of the wastewater used in the retention time of 3 hours had the highest Lead removal efficiency of about 77.45% and similarly, Chemically activated biochar had the Lead removal efficiency of about 74.51%.

Conclusion

The study tested three dosages (2g, 6g, 10g) of two types of activated biochar in 1 litre of wastewater at retention times of 1, 2, and 3 hours, totalling 18 treatments. Results showed higher dosages and longer retention times improved pollutant removal, with Physically activated biochar outperforming Chemically activated biochar. The optimal treatment was 10g of Physically activated biochar per litre at 3 hours, significantly reducing pollutant levels to safe discharge limits. Activated biochar proved to be a costeffective, eco-friendly solution for wastewater treatment. Further research on its toxicological impact is recommended for sustainable use.

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